Telephone system with selective code compression and register recycle



R. c. AVERY 3,131,262

18 Sheets-Sheet. 1

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Filed July 27, 1960 /NVENTOR R. C. AVERY BV kie, ATTORNEY Suk.

April 28, 1964 R. c. AVERY TELEPHONE SYSTEM WITH SELECTIVE CODE coMPREssIoN AND REGISTER RECYCLE 18 Sheets-Sheet, 6

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April 28, 1964 R. c. AVERY 3,131,262

TELEPHONE SYSTEM WITH SELECTIVE CODE COMPRESSION AND REGISTER RECYCLE 18 sheets-shewb Filed July 27, 1960 April 28, 1964 R. c. AVERY 3,131,262

TELEPHONE SYSTEM WITH SELECTIVE CODE COMPRESSION AND REGISTER RECYCLE 18 Sheets-Sheer, 9

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V: ou m Apnl 28, 1964 R. c. AVERY 3,131,262

TELEPHONE SYSTEM WITH SELECTIVE CODE COMPRESSION AND REGISTER RECYCLE Filed July 27, 1960 18 Sheets-Sheet. 10

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TELEPHONE SYSTEM WITH SELECTVE CODE COMPRESSION AND REGISTER RECYCLE 18 Sheets-Sheet 17 Filed July 27, 1960 E; Qu

/NVE/vron C. A VERY Bv JM L/ ATTORNEY April 28, 1964 R. c. AVERY TELEPHONE SYSTEM WITH sELEcTrvE conE COMPRESSION AND REGISTER RECYCLE Filed July .27, 1960 18 Sheets-Sheet 18 INVENTOR R. CAI/[RY /M @am ATTORNEY United States Patent D 3,l3l,262 TELEPHNE SYSEM lll-TH SlElillCllE CDE CMPRESSlN AND REGlSTEl-r RECYCLE Robert C. avery, .laclrson Heights, NSY., assigner to Bell 'eleplione `laboratories, incorporated, New York, NX.,

a corporation oi New ii/'erh Filed duly Z7, wel?, Ser. No. 45,766 l@ Claims. (Cl. 179-1S) This invention relates to telephone systems employing automatic switching equipment for the establishment of communication paths. ln particular, the invention provides new and improved means for handling customer dialed toll calls.

At the present time, there are plans for converting existing switching equipment to handle direct distance dialed calls, ereinafter referred to as DDD calls. The directing codes or digits required for such toll switching purposes have been arrived at by dividing the nation into areas, the size of each area generally depending upon the number of telephone stations therein, and each area being assigned a 3-digit area code. These 3-digit area codes are added to tue directory designations of each subscriber connected to the system. ln order to distinguish the S-digit area codes of a subscribers designation, the area code designations have been selected so as to have the second digit, of the 3 digits comprising each area code, always a l or a 0. The first digit of an area code may he any digit except a G or a 1, the being omitted since it might be confused with the digit O customarily dialed by a subscriber to reach an operator and the digit l being omitted to avoid the possibility of the false transmission of a l as the iirst digit through switchhoolr tumbling. The numbering plan currently in existence therefore provides that area codes may be XGX or XlX, where X is any of the digits 2 9 and in the third position may also include i).

Gne of the requisites for processing customer toll dialing is that the equipment in local central offices must be capable of receiving and registering l0 or l1 digit designations and of retransmitting them to a toll switching system. Certain of the automatic telephone systems presently in use, for example systems of the panel and crossbar type, initially were designed to receive and register only 7 or 8 digits of a subscriber number. These systems have subsequently been modified by the addition of auxiliary senders. ln general, an auxiliary sender circuit comrnon to a plurality of senders and is connectable thereto to provide additional register capacity in the event that a pretranslation of the first 3 digits indicates that the call is of a DDD variety.

ln a typical local automatic switching telephone ance, of the type known as a crossbar olllce, such as shown in United States Patent 2,235,803, granted to W. W. Carpeuter on March 18, 194i, when a subscriber originates a call the calling line is automatically connected to au idle district junctor and to an idle subscriber sender. The subscriber sender receives and registers called line designations as dialed by the calling subscriber but is equipped to register a maximum ot 8 digits. After the iirst 3 digits have been registered, identifying the ofce to which the cd1 is directed, the sender is connected to an idle marker and passes these 3 digits to the marker. The marker translates the digits into a routing indication from which it derives information which it uses in selecting ari idle trunk leading to the identified otlce and in connecting the selected trunk with the district junctor to which the calling line has already been connected. At the same time, the marker derives information required by the sender at the sending office as to the class of call, etc., which it passes back to the subscriber sender, followed by a release signal. From the class of call indication the subscriber sender determines the type oi outpulsing to be used in controlling the called oice, sets up the required type of control circuit passing by way of the district junctor and the selected outgoing trunk to the distant ollice and prepa es the proper pulsing equipment. This control circuit, which is used for both testing the condition of the trunk and for transmitting the designation to the distant oiilce, is usually called the fundamental circuit.

United States latent 2,867,690, granted to Charles O. Parks on lanuary 6, 1959, discloses an auxiliary sender arrangement which may or may not be inserted in the fundamental circuit in accordance with whether the call is to another toll area, herein called a foreign area, or is to the local area. Vith the addition of such circuitry therefore, DDD calls may be handled by local ollices which would otherwise have insuicient sender register capacity.

Prior to the institution of direct distance dialing in certain thickly populated areas of the country, for example, the area surrounding large cities, the density of telephone trahie required the establishment of special trunlring facilities within the areas themselves, in spite of the fact that relatively short distances were involved. When the areas for direct distance dialing purposes were established, it was found necessary to divide such thickly populated areas, placing a portion thereof in one DDD area and other portions in other DDD areas. Utilization of the standard central office modifications wherein aux: iliary sender registering equipment is used to aid in the establishment of calls between such DDD areas does not taire advantage of the many existing specialized trunk circuits.

A large proportion of the DDD calls emanating from any one area is directed to adjacent DDD areas. lt has been found that by distinguishing calls to adjacent DDD areas from calls to more remote DDD areas, it is possible to handle the majority of calls without requiring the use of auxiliary sender circuitry.

The present invention is designed to identify calls directed to predetermined areas and to expedite the handling thereof by routing them directly to the areas of destination and thereby avoiding the necessity for calling in auxiliary sender equipment. Because most of the existing local olhce equipment has been designed to register a maximum of 8 digit and direct distance dialed calls may require 10 or even 1l digits, an object of the invention is to provide a substitute for the auxiliary sender registers in the event the above-mentioned predetermined areas are dialed.

Another object of the invention is to recognize area designations of predetermined areas and to provide specialized handling of the connections required to establish the calls connected therewith.

Yet another object is to provide equipment having complete flexibility with respect to which area codes may be so handled.

The trend of telephone service indicates that in the future the numbering plan described hereinbefore may not furnish a sufficient number of discrete DDD areas in view of the anticipated volume or traiiic. This being so, it is very likely that codes other than those currently employed, i.e., of the form wherein a 0 or l in the second or B digit position signifies a DDD call, may be adopted to identify area codes.

lt is consequently another object of the invention to provide equipment with sufficient exibility to include the decoding and specialized treatment of calls preceded by codes ot the lXX or ABX variety.

The problem of register capacity is presented not only where DDD calls are involved, but also where special prefixes are used in addition to local call designations, for example, the premi 11. Should such prefixes be adopted to further identify the nature of DDD or other calls, as currently contemplated, the possible need for as many as 13 digit registers Yises.

Still another object of the present invention is to furnish equipment that permits the utilization of existing equipment with a minimum of modification to render it operable irrespective of the number of digits handled.

Gne desirable method for increasing capacity of existing equipment, in order to have it accomplish additional functions not originally contemplated, is to use the same equipment more than once in any cycle of operation. To date, in order to increase the capacity of standard switching systems, such as the panel and crossbar, which were designed for 8 digit directory numbers, auxiliary senders have been added. With the addition of auxiliary senders discrimination had to be made between local and DDD calls. Where DDD calls were detected the auxiliary senders were connected. The present invention discriminates not only between local and DDD calls, but also between general DDD calls and DDD calls to preselected areas. ln order to do this means are provided, when calls to the preselected areas are placed, for recycling the registers used for registering the first three digits of a dialed number, called the A, l, and G registers and registering the subsequently dialed office digits thereon.

The present invention features means operative upon detection of DDD area codes for seeking access to a decoder-translator whose function is to detect those calls destined for preselected areas and initiate specialized treatment thereof.

Circuits for reducing the number of registers needed to register a given number of digits are old in the art. Among these, are circuits having registers which alternately store a dialed number in one register section while a second section is transmitting a previously registered number, thereby making only two digit register sections necessary regardless of the number of digits involved. In such a circuit a digit register section may be restored in an interval required for the registration of one digit plus the interval between succeeding digits. Other circuir store some of the digits only and transmit others dhectly, thereby gaining additional time for restoration of the registers between uses.

A feature of the present invention is means for effecting the restoration of a plurality of register divit sections within the brief period between receipt of sequentially received digits.

Another feature resides in means activated upon detection of area codes for preselected areas, which recycle the A, B, and C registers to permit storage of subsequent digits before the fourth digit is received.

Another feature is the means whereby the area codes associated with remote DDD areas are detected, and auiliary senders called in, without the use of pretranslating equipment.

till another feature of the invention is means for interrupting the marker start signaling apparatus upon determination that a DDD call is to one of a plurality of preselected areas.

Another feature of the invention is a group of high speed relay decoder-translator circuits which permit numerous area codes to be handled within an interdigital time period.

Another feature of the invention is a relay decodertranslator eEective to rapidly perform decoding and translating functions with a minimum of circuitry and with high efliciency.

Another feature of the invention resides in means for automatically monitoring the code .compression process and signaling the cause of failure if a failure should occur.

Basically, the invention employes a code compressor in conjunction with an automatic telephone switching system,

to detect the registration of preselected DDD area codes in the A, B, and C registers of a sender. The compressor is connected to a register wherever a DDD number is detected by the presence of a 0 or l digit in the second, or B section, of the register. lf the area code does not identify an adjacent area, and therefore is not among those preselected, an auxiliary sender is called in to handle the calls as in earlier circuits. lf the area code identifies an adjacent area, and the code is therefore one of a preselected group of codes, the compressor initiates the establishment of a direct connection over trunking circuits to the area identified thereby and also recycles the A, B, and C sections of the register in time to permit registration f the fourth, fifth, and sixth digits therein. The circuitry yis thus arranged to permit the decoding of codes on the first 3 registers and the recycling thereof during the interdigital time period.

The foregoing as well as additional objects and features will be clemly understood from the following description made in conjunction with the drawings wherein:

FIG. 1 is a block diagram of an embodiment of the invention;

FIG. lA shows the manner in which the circuit schematic sheets should he arranged;

FGS. 2 and 3 are circuit schematics of typical recycle circuits as connected for example to elements of a crossbar subscriber sender;

FlGS. 49, 14 and l7 are circuit schematics of portions of the connector circuitry;

FIGS. lll-13, l5 and 16 are circuit schematics of the compressor arrangement including three decoder-translators which serve a bloeit of 20() subscriber senders; and

lllG. 18 is a sequence chart showing the normal sequence of operation of the disclosed circuitry upon receipt of a regular DDD call.

For purposes of description the present invention is disclosed as embodied in a typical crossbar switching system, such as described in the aforementioned Carpenter patent, 2,23 5,863, in cooperation with the auxiliary sender circuitry described in the aforementioned Parks Patent 2,867,690, modied as necessary to perform the functions and afford the features described in the foregoinG as well as hereinafter. It should be understood, however, that the teachings herein are also applicable, with minor modifications, to panel systems.

The basic circuit units and their functional interrelationships may be recognized and understood from a consideration of FIG. l, wherein it may be seen that the illustrative embodiment contains circuitry for providing preselected area code compression for two hundred subscriber senders. Each individual sender 2lb@ is connected to a distinct recycle circuit 263i. A group of ten senders is served by one connector circuit lili? and access thereto is obtained via a sender preference circuit '/"ll, individual thereto. Each connector circuit dlltl, in turn, has access to three decoder translators 12Go, 15%, or ldl. in order to determine which connector will first be served and which compressor will be employed, connector preference circuits dill, SdZ, and il, and compressor selector i5-titl, are provided, respectively.

When any DDD code is dialed into a subscribed sender, the registration of the O or l in the B digit register activates the subscriber sender recycle circuit. Upon activation, the recycle circuit initiates opening of the marker start lead to prevent passage of these code digits thereto for translation or other operations; actuates the sender preference circuit thereby bidding for access to the common connector serving its sender group; and applies a start signal to the compressor selecting circuits to secure the services of an idle compressor, As will be noted in the following description, the latter two operations are performed coincidently in order to minimize the total operating time.

The sender pre erence circuits insure access to the connector serving their group of subscriber senders according 

7. A TELEPHONE SYSTEM WHEREIN CALL ROUTING IS RESPONSIVE TO AREA CODE DESIGNATIONS COMPRISING A FIRST PLURALITY OF SEQUENTIALLY RECEIVED DIGITS AND LINE ADDRESS CODE DESIGNATIONS COMPRISING A SECOND PLURALITY OF SEQUENTIALLY RECEIVED DIGITS; COMPRISING MEANS FOR REGISTERING EACH DIGIT OF SAID FIRST PLURALITY, TRANSLATING MEANS RESPONSIVE TO THE REGISTRATION OF CERTAIN PRESELECTED ONES OF SAID AREA CODE DESIGNATIONS, AND MEANS CONTROLLED BY SAID TRANSLATING MEANS AND OPERATIVE BEFORE THE RECEIPT OF SAID SECOND PLURALITY OF DIGITS FOR SIMULTANEOUSLY RECYCLING EACH OF SAID REGISTERING MEANS TO RECEIVE SAID SECOND PLURALITY OF DIGITS. 